The intertwined epidemics of obesity and diabetes have produced a public health crisis that demands an improved understanding of fat biology and metabolism. Through genetic screens in C. elegans and D. melanogaster, we identified many genetic regulators of invertebrate fat storage/metabolism that also have a conserved role in mammals. We focused our attention on one gene, Adipose (Adp), because its striking anti-obesity and anti-diabetes function in worms, flies, and mammals highlight its importance in metabolism and potential as a therapeutic target. The goal of this proposal is to unravel the physiological and molecular mechanisms underlying these striking effects. Our hope is that these metabolic and molecular studies will enhance our understanding of mammalian metabolism and lead to novel therapeutic strategies for obesity and diabetes. Adp regulates an ancient metabolic pathway. Reducing Adp function in worms, flies, mammalian adipogenic cells, and mice stimulates fat formation (obesity) and Adp mutant flies and mice have diabetes. These effects result from actions of Adp within adipocytes, as adipocyte-restricted expression of dominant negative Adp in mice caused obesity and diabetes. Conversely, fat selective expression of wild-type Adp produces lean, glucose sensitive flies and mice. Yet, there remain several unexplored issues relating to the in vivo metabolic phenotypes. In Aim I, we will characterize the metabolic physiology of our various invertebrate and mouse models in which Adp action is modified. These studies will rigorously test our hypothesis that altered energy expenditure underlies the anti-obesity actions of Adp. Then, we will examine how Adp regulates the responses to high fat diet and other metabolically relevant stimuli (Aims I and II). In parallel (Aim III), we unravel the molecular mechanisms underlying the Adp effects. Our initial studies show that Adp binds to and functions with several Adp interacting proteins (AIPs) that regulate chromatin dynamics and gene transcription. A unifying mechanism for how Adp regulates these AIPs stems from our data that Adp appears to control the substrate specificity of a novel ubiquitin E3 ligase complex. In Aim III, we will characterize the role that this E3 ligase has in fat biology; knowledge that is key in order to develop the fundamental insights required to ultimately manipulate the Adp pathway for therapeutic ends.